This group of disorders is also known as conversion hysteria. The term "hysteria" is a controversial one and is used in several different ways; as a result it has been omitted from both DSM-IV and ICD-10 but it is still widely used as a diagnostic category in clinical practice.
Dissociative disorders are characterised by symptoms that suggest lesions in the motor or sensory pathways of the voluntary nervous system. There is loss or distortion of neurological function which cannot be adequately accounted for by organic disease.40 Psychiatrists would also want to establish positive evidence that the symptom is linked to psychological factors,41 either previous severe stress, emotional conflict, or an associated psychiatric disorder. It is assumed that the symptoms are not intentionally produced, as in malingering, but are a result of unconscious motives. This, however, is a notoriously difficult distinction to make and it often appears that the degree of insight into the nature of the disability varies from time to time.
Dissociative disorders are thought to be declining in incidence. The commonest symptoms, which are usually of acute onset, are motor weakness, altered sensation, gait disturbance, and pseudo-seizures.42 The neurological examination reveals characteristic abnormalities that enable the experienced neurologist to make a confident diagnosis in most cases.43 Weakness usually involves whole movements rather than muscle groups and it affects the extremities much more often than ocular, facial, or cervical movements. Various clinical techniques can be employed to show that weakness of a limb is associated with simultaneous contraction of opposing muscle groups. There is discontinuous resistance during testing of power ("give way weakness"), muscle wasting is absent, and reflexes are normal. Sensory loss or distortion is often inconsistent when tested on more than one occasion and incompatible with peripheral nerve or root distribution. There may be discrete patches of anaesthesia or hemisensory loss which stops abruptly in the midline. Visual symptoms include monocular diplopia, triplopia, field defects, tunnel vision, and bilateral blindness associated with normal pupillary reflexes. Dissociative gait disturbance, astasia-abasia, is recognised by its bizarre character and intermittent pattern; the patient walks normally if he or she thinks that no one is observing. In some cases, when being observed, the patient actively attempts to fall and this contrasts with the patient with organic disease who tries to support him- or herself.
Pseudo-seizures are more difficult to evaluate because they are episodic and often coexist with true epilepsy. An account from a reliable observer is invaluable but it is essential for the clinician to witness an attack before making a firm diagnosis. The clinical features, which simulate epilepsy to a varying degree, have been described in detail.44 During an attack there is marked involvement of the truncal muscles with opisthotonus and lateral rolling or jerking of the head and body. All four limbs may exhibit random thrashing movements which increase in amplitude if restraint is applied. Cyanosis is rare unless there is deliberate breath holding. Corneal and pupillary reflexes are retained although they may be difficult to elicit because the eyelids are kept firmly closed. Tongue biting and urinary incontinence are uncommon unless the patient has some degree of medical knowledge and has learned from experience that they are characteristic features of epilepsy.
In contrast to true epilepsy, pseudo-seizures usually occur in the presence of other people and not when the patient is alone or asleep. Some episodes simulate partial motor seizures or simple faints. Others occur in rapid succession without recovery of consciousness and they may be accompanied by deliberate tongue biting or incontinence so the clinical picture mimics status epilepticus. In addition to the clinical features of the attacks, certain demographic characteristics help to distinguish pseudo-seizures from true epilepsy. Patients with pseudo-seizures are more likely to have a family history of psychiatric illness, a personal history of psychiatric illness, previous suicide attempts, sexual maladjustment, and current affective disorder.45
Dissociative, or psychogenic, amnesia can also create diagnostic problems.46 There is a sudden loss of memory, usually in relation to a markedly stressful event. The amnesia is selective and predominantly involves the inability to recall emotionally charged memories. The ability to learn new information is relatively preserved, as are cognitive skills such as reading and writing. A characteristic feature is a loss of personal identity; the patient is unable to recall his or her name, age, address, occupation, and family details, and may fail to recognise relatives when they visit. Recovery is usually rapid and complete. In some cases, however, dissociative amnesia lasts for several days or weeks and is accompanied by an apparently purposeful wandering away from the home or place of work. During this condition, known as a dissociative fugue, a new name and identity may be assumed. Self-care is maintained and the patient's behaviour may appear completely normal to people who do not know him or her. Recovery occurs abruptly and there is amnesia for the period of the fugue. Organic conditions that need to be considered in the differential diagnosis of dissociative amnesia include head injury, delirium, epileptic fit, Wernicke's encephalopathy, alcoholic blackout, and transient global amnesia.
Any patient suspected of having dissociative symptoms should be examined carefully by a neurologist and psychiatrist. Special investigations, such as MRI and EEG telemetry, are required in some cases before a confident diagnosis can be made and, in a few, a decision has to be deferred until the symptoms can be reviewed after a suitable time interval. The presence of organic disease does not rule out a diagnosis of dissociative disorder. Indeed it is now recognised that neurological lesions and dissociative symptoms occur together more frequently than can be explained by chance. Although the neurological lesion cannot explain the presenting symptom, coexisting disease of the nervous system may facilitate the emergence of dissociative mechanisms and provide a model for the symptom.40 This may explain the frequent occurrence of pseudo-seizures in patients who also have genuine epilepsy.
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